Flooring Tile - Can yo utile over existing tile?

I've seen some people do it and was wondering if possible or not.

If the answer is no, then what is the most effective way of removing the old tile and getting the floor "right" for the new tile.

If the answer is yest, is the procedure the same as tiling over concrete?

FYI, it's a concrete slab underneath the tile. Would I have to install durock or hardy board?

Thanks

Tile over tile can be done. Take into consideration increased height of floor and effects it will have on trim and transition pieces to adjacent floor coverings. Glossy tiles are not a good candidate for tile over tile and should be torn out. For large areas, a pneumatic chisel can be used. Loose tiles have to be removed and areas filled with leveling compound. Existing tiles have to be thoroughly clean and free of soil, grease, scum, wax, sealers, and anything that would interefere with the bond. Surface should be lightly sanded to improve bond of thinset. Concrete underlayment board is not installed over concrete subfloor.